We intend to explore the effects of ischemia on the electrolyte content (Na, Mg, P, S, Cl, K, Ca) of intra- and extracellular compartments in myocardial cells. In spite of the importance of these cellular ionic changes to the basic understanding of cell injury and death, such a study as proposed here has only recently become possible with the development of the new techniques of X-ray microanalysis and morphometry. Three experimental conditions will be examined: in vitro ischemia (also called autolysis), in vivo ischemia and in vivo ischemia with reflow. We have performed preliminary experiments which indicate that quantitative differences in electrolyte shifts do exist between these experimental conditions, possibly depending upon the available extracellular space. The proposed studies will include ultrastructural assessment of myocardial cells, morphometry using the criteria developed by the International Society of Stereology, elemental analysis by x-ray microprobe of unfixed ultrathin frozen-dried myocardial sections and measurements of metabolite levels such as adenine nucleotides and lactate. The questions under study will include study of the electrolyte fluxes that occur in the three experimental conditions between the electrolyte fluxes that occur in the three experimental conditions between extracellular space and cytosol and between mitochondria and cytosol as a function of time and how these changes correlate with intracellular metabolism, particularly the levels of high energy adenine nucleotides. Insight into these intracellular events is important because organelle function is suspected of being closely coupled to specific changes in the internal environment. Particular attention will be paid to the role of calcium which we consider a key event in cell destruction and to magnesium and potassium which apparently are closely related to intact oxidative phosphorylation. Furthermore, we hope to uncover the critical events which take place in cell survival.